OBJECTIVES: 1) Continue work to define the amino acids to which selenocysteine in glutathione peroxidase is attached and the sequence of the amino acids around it in the polypeptide chain. 2) Continue purification of glutathione peroxidase and other selenoproteins by HPLC, electrophoresis and other chromatographic techniques. 3) Study other selenoproteins than glutathione peroxidase in rat tissues to determine subcellular localization and/or to determine whether they all contain selenium as selenocysteine. 4) Study a plasma selenoprotein and determine if it is a carrier of selenium. 5) Study selenium and nonselenium glutathione peroxidase in a variety of animal species and tissues. 6) Complete studies on a selenocysteine tRNA of rat liver.